Selective catalytic reduction (SCR) is used for the oxides of nitrogen (NOx) reduction in internal combustion engine exhaust. The efficiency of NOx reduction of an SCR catalyst is based upon the temperature of exhaust gases being exposed thereto. Exhaust gases are typically at low-efficiency temperatures during low-load conditions. Heat sources have been used to raise the temperature of the exhaust gases to a level allowing the SCR catalyst to perform more efficiently.